A virtual private network (VPN) refers to a communication network which uses public network resources to provide private network capabilities without necessarily using dedicated network resources. Subscriber lines connected to different network exchanges, constitute a virtual private network that may include private network capabilities, such as contact restrictions, private addressing plan, tunnelling, and/or encryption.
A VPN gateway (virtual private network gateway) refers to an integrated firewall and/or a virtual private network (VPN) hardware device that includes static routing functions and provides secure end-to-end VPN connections between sites. The VPN gateway may be used for the secure connection of a company's central site and branch offices as well as for connecting a company with its partners, customers, or subcontractors. The VPN gateway implements an IP security standard, secured internet protocol (IPSec), and internet key exchange (IKE) key management. It also supports network address translation (NAT).
One of the problems associated with the above arrangement is that in situations where two or more different VPN technologies are used and have conflicting IP addresses, an overlapping customer network prevents more than one VPN to be active at the same time because of the overlapping IP addresses. Thus, only a single VPN tunnel can be up at the same time. The situation of conflicting IP addresses may be managed by defining the remote networks such that they are not overlapping. However, construction and management of such a system is complicated.